Healthcare-Associated Infections — Viva

Long Case Viva Defence

Candidate's opening statement (model answer)

"Mr Robert Chen is a 68-year-old retired engineer who is on day 7 of his ICU admission following an emergency laparotomy for a perforated sigmoid diverticulum, and who now presents with dual device-associated healthcare-associated infections — a Pseudomonas aeruginosa catheter-related bloodstream infection from his right internal jugular central line, confirmed by paired blood cultures with a differential time to positivity above 120 minutes, and a concurrent ventilator-associated pneumonia from the same organism grown from his endotracheal aspirate. He has been intubated and ventilated since admission, has a central line, a urinary catheter, and a clean midline laparotomy wound, and he received 5 days of piperacillin-tazobactam postoperatively. [1]

His main problems are:

1. Pseudomonas aeruginosa catheter-related bloodstream infection requiring immediate line removal.
2. Concurrent Pseudomonas ventilator-associated pneumonia.
3. Prolonged ICU admission with ventilator dependency and the risk of further device-associated complications.
4. Recent broad-spectrum antibiotic exposure (5 days of piperacillin-tazobactam) with the attendant risks of Clostridioides difficile and further selection of resistant organisms.
5. The underlying surgical condition (perforated diverticulum) and the need to exclude ongoing intra-abdominal source. [1]

His management has been to obtain cultures before starting targeted therapy (the organism and sensitivities were known from the initial cultures), remove the central line and send the tip for culture, insert a new line at a different site for ongoing access, start targeted anti-pseudomonal therapy based on the sensitivity results, apply the ventilator bundle to prevent further complications, and plan a daily review of antibiotic need and device necessity. His plan is to complete a 14-day course of targeted therapy (with repeat blood cultures until clearance), to wean and extubate as soon as possible, to conduct a stewardship review of the preceding antibiotic exposure, and to document the case for the unit's HAI surveillance and prevention programme." [1]

Examiner probing questions and model answers

Q1: "Walk me through how you confirmed that the central line was the source of the bacteraemia rather than the pneumonia." [1]

"The key diagnostic test is the paired blood culture strategy with differential time to positivity. Two sets of blood cultures were drawn before antibiotics — one peripherally and one through the central line. Both grew the same organism (Pseudomonas aeruginosa with the same sensitivity pattern), which confirms bacteraemia and excludes contamination. The differential time to positivity — the time between the central line culture turning positive and the peripheral culture turning positive — was more than 120 minutes (the central culture was positive 3 hours before the peripheral). This strongly supports the catheter as the source, because a higher bacterial inoculum is present in the blood drawn through the infected line, so it reaches the detection threshold sooner [3]. The differential time to positivity has a sensitivity above 80 per cent and a specificity above 90 per cent for catheter-related bloodstream infection.

Now, the question of whether the line is the primary source and the pneumonia is secondary (haematogenous seeding to the lungs), or whether the pneumonia is the primary source and the line is secondary (bacteraemia from the lungs seeding the catheter biofilm), is clinically interesting but does not change the immediate management — both foci must be treated. In this case, the fact that the line culture turned positive first (positive DTP) favours the line as the primary source, with the pneumonia potentially representing either independent VAP from the same organism (the patient has multiple risk factors — prolonged intubation, broad-spectrum antibiotics, supine position) or haematogenous seeding. The practical point is that the line must be removed regardless, because Pseudomonas forms biofilms that cannot be eradicated with antibiotics alone [3]."

Q2: "Why did you remove the line rather than attempt antibiotic lock therapy? When is line salvage appropriate?" [1]

"Line salvage with antibiotic lock therapy is appropriate for a very limited set of organisms and circumstances. The IDSA guideline recommends attempting line salvage only for low-virulence organisms — primarily coagulase-negative staphylococci and, in some circumstances, enterococci — in patients where line replacement is difficult (e.g., limited venous access from previous lines, thrombosis, or anatomical constraints). Even for coagulase-negative staphylococci, the success rate of antibiotic lock therapy is only 60 to 70 per cent, and the patient must be monitored closely with repeat blood cultures. [1]

Line salvage is NEVER appropriate for Staphylococcus aureus, Pseudomonas aeruginosa, or Candida species. These organisms form particularly resilient biofilms, carry a high risk of metastatic infection (endocarditis, osteomyelitis, septic emboli), and attempted salvage is associated with high rates of persistent bacteraemia, relapse, and treatment failure [3]. In this patient with Pseudomonas bacteraemia, removing the line is non-negotiable. Antibiotic lock therapy works by instilling a high concentration of antibiotic (typically 100 to 1000 times the MIC) into the catheter lumen for hours or days, in addition to systemic therapy, to eradicate the biofilm within the lumen. But it only addresses the intraluminal biofilm — if there is an extraluminal biofilm on the outer surface of the catheter, or a tunnel tract infection, lock therapy cannot reach it. This is another reason why salvage fails for virulent organisms — their biofilms are not confined to the lumen."

Q3: "The patient has been on the ventilator for 7 days. What is your strategy to prevent further ventilator-associated events, and when would you attempt to extubate?" [1]

"The strategy is to apply the ventilator bundle reliably and to assess for readiness to extubate every day. The ventilator bundle components are: head of bed elevation to 30 to 45 degrees (the single most effective measure for preventing microaspiration); daily sedation interruption with a spontaneous breathing trial (the 'wake up and breathe' protocol, which reduces the duration of mechanical ventilation and allows early identification of patients ready for extubation); oral chlorhexidine (reduces oropharyngeal bacterial load, though the 2022 SHEA and IDSA Compendium reduced the emphasis on this); subglottic secretion drainage if the endotracheal tube has a suction port; peptic ulcer and DVT prophylaxis as part of the overall ICU care bundle; and daily review of the need for ongoing intubation [4].

For the extubation assessment, I use a structured daily protocol: first, assess whether the underlying condition that required intubation is improving (in this case, the intra-abdominal sepsis should be resolving, the pneumonia should be improving with antibiotics); second, perform a sedation interruption to assess the patient's neurological status (is the patient awake and cooperative?); third, perform a spontaneous breathing trial (reduce or stop the ventilator support and observe whether the patient can maintain adequate gas exchange without respiratory distress for 30 to 120 minutes — looking at respiratory rate, tidal volume, oxygen saturation, heart rate, blood pressure, and subjective effort); and fourth, assess airway protective reflexes (cough, gag, ability to manage secretions) before extubating. The daily spontaneous breathing trial is the key intervention — it reduces the duration of mechanical ventilation by an average of 2 to 3 days and reduces VAP, because every additional day of ventilation increases the VAP risk by approximately 1 per cent per day in the early period [4].

The subglottic secretion drainage component deserves comment — the Muscedere meta-analysis of 13 randomised trials showed a pooled relative risk of 0.55 for VAP, with reductions in duration of ventilation and ICU stay [5]. If the current endotracheal tube does not have a subglottic suction port, I would not routinely exchange the tube just to get this feature (tube exchange carries its own risks, including reintubation, which is itself a VAP risk factor), but I would ensure subglottic suction tubes are used for all new intubations expected to last more than 48 to 72 hours."

Q4: "He received 5 days of piperacillin-tazobactam postoperatively. What stewardship lessons are there, and does the Pseudomonas infection relate to this exposure?" [1]

"There is a strong stewardship lesson here. The preceding broad-spectrum antibiotic exposure is almost certainly relevant to the Pseudomonas infection — piperacillin-tazobactam is an anti-pseudomonal beta-lactam, and exposure to it selects for Pseudomonas colonisation of the patient's oropharynx and gut, which then seeds the endotracheal tube (causing VAP) and potentially the central line hub (causing CRBSI). This is the classic mechanism of antibiotic-selected HAI: broad-spectrum antibiotics disrupt the normal protective flora and select for resistant or virulent organisms that then cause device-associated infection. [1]

The stewardship review should address: was the initial piperacillin-tazobactam appropriate? (For perforated diverticulum with peritonitis, empiric broad-spectrum cover including anti-pseudomonal and anaerobic cover IS appropriate — this is the right initial choice.) Was it de-escalated when culture results returned? (Intra-abdominal cultures from the surgery should have guided de-escalation — if the intra-abdominal organisms were susceptible to narrower agents like ceftriaxone plus metronidazole, the piperacillin-tazobactam should have been narrowed.) Was it stopped at the appropriate time? (For complicated intra-abdominal infection with source control, 4 to 7 days is typically adequate — 5 days is appropriate if the patient was improving.) Was there an opportunity for earlier IV-to-oral switch? (Not in this patient, who was critically ill in the ICU.) [1]

The broader stewardship lesson is that every antibiotic prescription has consequences — not just for the patient (selection of resistant organisms, C. difficile risk) but for the ward (selection pressure favouring MDR organisms that can spread to other patients). The five rights of stewardship — right drug, right dose, right route, right duration, right indication — apply here. And the 48-hour review is the key intervention: at 48 hours, when intra-abdominal cultures return, the team should have reviewed the indication, the spectrum, and the plan for duration, and narrowed or stopped the therapy if appropriate [6]."

Q5: "How would you counsel the family about what has happened and the road ahead?" [1]

"I would sit down with Mr Chen's wife and adult children, with the ICU nurse present, and explain clearly and honestly. I would tell them that Mr Chen developed two infections related to the devices he needed for his critical care — an infection in his intravenous line and a chest infection from the breathing tube — and that both are caused by a bacterium called Pseudomonas that is common in hospitals and particularly affects patients who have been on antibiotics and in intensive care for some time. I would explain that we have identified the infections early through the blood tests and the lung samples, that we have removed the infected intravenous line and replaced it with a new one, that we have started an antibiotic targeted to the specific bacterium, and that we are applying all the measures we know to help him come off the breathing machine as soon as possible. [1]

I would be honest that this is a setback in his recovery from the emergency surgery, that the Pseudomonas infection is serious, and that he will need close monitoring in the ICU for the coming days. I would discuss the expected timeline — the antibiotics will continue for approximately 2 weeks, the focus is on getting him strong enough to come off the breathing machine, and the surgery is healing well. I would ask about his values and goals — would he want to remain on the breathing machine indefinitely if recovery is very slow, or are there limits to the intensity of treatment he would want? I would offer to bring the surgeon and the intensivist to a family meeting, and I would ensure the family has a clear point of contact (the ICU nurse coordinator) for questions and updates. The communication is part of the treatment — a family that understands the situation and the plan can support the patient, participate in decisions, and cope with the stress of critical illness." [1]